1. Field of the Invention
The present invention relates to an air conditioning system, and more particularly, to a method for controlling a multi-unit air conditioning system, wherein the operating times of compressors are uniformly controlled to lengthen the lifespan of the air conditioning system.
2. Discussion of the Related Art
Generally, air conditioning systems perform procedures of compressing, condensing, expanding and evaporating a refrigerant to cool and/or heat a confined space.
Such air conditioning systems are classified into a cooling type wherein a refrigerant flows only in one direction through a refrigerant cycle, to supply cold air to a confined space, and a cooling and heating type wherein a refrigerant flows bi-directionally in a selective manner through a refrigerant cycle, to selectively supply cold air or hot air to a confined space.
Also, such air conditioning systems are classified into a general type wherein one indoor unit is connected to one outdoor unit, and a multi-unit type wherein a plurality of indoor units are connected to one outdoor unit.
One or more compressors are installed in the outdoor unit of such a multi-unit air conditioning system.
In a multi-unit air conditioning system wherein a plurality of compressors are installed, the number of compressors is adjusted in accordance with the amount of refrigerant required in the system.
For example, where the number of indoor units to operate is small, the number of compressors to operate is reduced, whereas if the number of indoor units to operate is large, the number of compressors to operate is increased.
Also, when the temperatures of all confined spaces, for example, all room spaces, to be air-conditioned, satisfy a predetermined temperature range, all compressors, which are in operation, are turned off.
Meanwhile, when only a part of the room spaces exhibit a temperature satisfying the predetermined temperature range, only a part of the compressors, namely, the associated compressors, which are in operation, are turned off.
Also, when the room space or room spaces, which have exhibited a temperature satisfying the predetermined temperature range, subsequently do not satisfy the predetermined temperature range, the associated compressor or compressors are operated again.
However, the above-mentioned conventional multi-unit air conditioning system has the following problems.
First, in the conventional multi-unit air conditioning system, when a part or all of the compressors are turned on again after being turned off, the turning-on of those compressors is controlled to be sequentially carried out, starting from a particular one of the compressors.
For this reason, there is a problem in that the particular compressor, which is always turned on first, is reduced in lifespan, as compared to the remaining compressors.
Second, the operating time of the particular compressor, which is always turned on first, is much longer than those of the remaining compressors. For this reason, there is a problem in that, if the lifespan of the particular compressor is substantially exhausted, the outdoor unit itself or the system itself must be replaced even though the lifespan of the remaining compressors is sufficient.
This is because the system cannot generally operate with a sufficient performance under the condition in which the lifespan of even one compressor is substantially exhausted, and it is necessary to replace the outdoor unit itself or the system itself unless the cause of the degradation in system efficiency can be found.
Third, since the lifespans of the compressors are non-uniform, the performances of the indoor units are non-uniform. For this reason, the time taken for the process of repairing the system and the number of times to perform the repairing process are increased.
As a result, the maintenance and repair costs of the system increases. Furthermore, a remarkable degradation in the reliability of the system occurs.
Fourth, since the sequence of turning on the compressors is fixed, there is a problem in that the lifespan difference between the compressor, which is always turned on first, and the compressor, which is always turned on last.